FS#329 - Editable focal lengths and apertures

The ability to edit/add focal lengths and apertures from within PO's GUI instead of having to edit common.php. I had to add 170 and 200 as focal lengths and 6.7 as aperture for my lenses.

Maybe simply select "Custom" in the drop-down box and have a nearby text field to write-in custom values?
Or, for starters, break out these arrays to a separate site-specific file that won't get over-written with an update?